Semiconductor wafers must be accurately placed within the focal region of lithography tools within tight tolerances to properly write features having narrow linewidths and high densities. Focus-sensitive metrology targets are specialized marks patterned onto the wafer during a lithography step in which one or more characteristics of the mark (e.g. alignment of two features) is indicative of the focal position of the wafer during the lithography step. Focus sensitive metrology targets are typically generated as images of pattern masks generated by the lithography tool. In this way, focus-sensitive pattern masks contain one or more pattern elements that, when imaged on the wafer, provide measurably distinct variations corresponding to deviations of the focal position of the wafer from a nominal focal position.
Further, it is desirable that pattern masks used to generate focus-sensitive metrology targets to be used in a semiconductor fabrication line be cost-effective and integrate with the pattern masks used to write the semiconductor devices under production. Therefore, it would be desirable to provide a system and method for curing defects such as those identified above.